Add shared javascript VMs and demo config

provider/javascript/init.go

@@ -0,0 +1,56 @@
+package javascript
+
+import (
+	"github.com/andig/evcc/util"
+	"github.com/robertkrimen/otto"
+)
+
+// Configure initializes JS VMs
+func Configure(other map[string]interface{}) error {
+	cc := []struct {
+		VM     string
+		Script string
+	}{}
+
+	if err := util.DecodeOther(other, &cc); err != nil {
+		return err
+	}
+
+	// init all VMs that require it
+	for _, conf := range cc {
+		if conf.Script == "" {
+			continue
+		}
+
+		if _, ok := registry[conf.VM]; !ok {
+			vm := otto.New()
+
+			_, err := vm.Run(conf.Script)
+			if err != nil {
+				return err
+			}
+
+			registry[conf.VM] = vm
+		}
+	}
+
+	return nil
+}
+
+var registry = make(map[string]*otto.Otto)
+
+// RegisteredVM returns a JS VM. If name is not empty, it will return a shared instance.
+func RegisteredVM(name string) *otto.Otto {
+	vm, ok := registry[name]
+
+	// create new VM
+	if !ok {
+		vm = otto.New()
+
+		if name != "" {
+			registry[name] = vm
+		}
+	}
+
+	return vm
+}